JP3360792B2 - Scanning probe microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope in which a control deviation of a control system is positively utilized.
The present invention relates to a scanning probe microscope suitable for scanning a probe at a relatively high speed and quickly capturing information on a sample surface.

[0002]

2. Description of the Related Art A scanning probe microscope (hereinafter "SPM")
Is referred to as a probe with a pointed tip approaching the sample to the order of nanometers (nm). At that time, physical interaction such as atomic force generated between the probe and the sample occurs. This device measures the shape of the sample surface and the like at the atomic dimension level by measuring the action. Among them, a force microscope represented by a scanning atomic force microscope (hereinafter also referred to as “AFM”) uses a cantilever having a very low spring constant and has a very low spring constant between a probe provided at the tip of the cantilever and a sample. This device measures the amount of displacement of the cantilever due to the bending deformation of the cantilever due to the atomic force acting on the sample, thereby measuring the uneven shape of the sample surface.

With reference to FIG. 5, a description will be given of a configuration of a typical mechanical main part of a conventional AFM and a configuration of a control system. This A
FM is a general contact mode AFM. The operation of measuring the shape of the sample surface by the AFM is as follows.

A cantilever 52 having a probe 51 at its tip
Is measured by an optical displacement detection device called an optical lever comprising a laser light source 53 and a photodetector 54. The optical lever is generally widely used as a cantilever displacement detecting unit of the AFM. The tripod 55 includes piezoelectric elements 58a and 58b (Y-axis piezoelectric elements are not shown) in three axes (X, Y, and Z axes orthogonal to each other) supporting a sample table 57 on which the sample 56 is mounted. , X
This is a three-dimensional actuator for performing scanning in the Y direction and operation in the Z-axis direction for controlling the distance between the probe and the sample (or between the cantilever and the sample).

When measuring the surface shape of the sample 56,
The cantilever 52 having the probe 51 is brought closer to the region where the atomic force acts on the sample 56 by an approach / retreat mechanism (not shown). At this time, the probe 51 receives a force from the surface of the sample 56, and the cantilever 52 bends and deforms. When the bending deformation of the cantilever 52 occurs, the displacement amount (probe 51) due to the bending deformation of the cantilever 52 detected by the optical lever is detected by the subtractor 59 and the control circuit 60.
The displacement of the tripod 55 in the Z-axis direction is controlled such that the deviation signal Δs as the difference between the displacement signal s1 representing the displacement amount of the tripod and the preset set value s0 becomes zero.
That is, the amount of displacement of the cantilever 52 due to the bending deformation is controlled so as to always coincide with the set value s0. Therefore, the probe 51 is kept pressed against the sample 56 with a constant force. When the piezoelectric element of the tripod 55 is driven by the XY scanning circuit 61 to scan the surface of the sample 56 while controlling the pressing force to be constant, the control signal s2 in the Z-axis direction becomes uneven on the surface of the sample. Will change accordingly. Based on the control signal s2 and the output signal of the XY scanning circuit 61, the signal processing device 62 can obtain information on the uneven shape of the sample surface, thereby displaying a measurement image on the display device 63.

In an actual apparatus, a value at which the control signal s2 changes is used as height information of each point in the scanning range of the sample 56, and for example, a contrast of light and shade is added to the display screen according to the height. By displaying, the shape of the measurement area of the sample is visually represented.

A scanning tunneling microscope (STM), which is one of the SPMs, detects a tunnel current that changes according to the distance between a probe and a sample, and the value of the tunnel current matches a preset value. To control the distance between the probe and the sample. Although the detected physical quantities are different, the AFM and the control signal are similar, and the principle of measurement is almost the same. The same applies to other types of scanning probe microscopes.

[0008]

In observing the sample surface, in the conventional SPM, first, an observation is performed quickly in a relatively large scanning range to find a target observation location, and the target location is reduced to a smaller scanning range. For example, a technique of observing at a higher resolution, and further reducing the scanning range and further increasing the resolution to perform detailed observation as necessary has been used. Considering this as a substitute for a general optical microscope, first, observe the target place broadly and broadly with a low-magnification objective lens, increase the magnification, and increase the resolution of the target place for observation. Work to improve (zooming)
Is equivalent to

However, in the configuration of the conventional SPM control system, if a large scanning range is to be scanned at high speed,
There is a high possibility that the control for keeping the distance between the probe and the sample surface constant cannot follow the change in the unevenness of the sample surface. According to the conventional SPM configured to obtain information on the sample surface using a control signal for controlling the distance between the probe and the sample to be constant, accurate measurement cannot be performed when control cannot be followed. In some cases, it may not even be possible to capture the general shape of the sample surface. Therefore,
In such a case, the scanning speed must be reduced and the measurement must be performed slowly and slowly, and the purpose of quickly observing a large scanning range cannot be achieved.

In the SPM, it is very common that the sample is inclined and placed on the sample table. In the conventional SPM, the unevenness of the sample surface and the inclination when the sample is placed are similarly measured as a change in the control signal corresponding to the change in height. Therefore, height information including both the unevenness of the sample surface and the inclination of the sample is displayed as, for example, black and white shading information. If the inclination of the sample is relatively larger than the size of the irregularities on the surface of the sample to be observed, only the inclination of the sample can be recognized from the image displayed as the observation result, and the irregularities on the surface can be recognized. This is a problem because the reflected contrast of light and shade cannot be recognized.
In general, the roughness of a sample to be observed by SPM is several μm at most, and it is often desired to observe the roughness at the nm level. Therefore, it can easily occur that the inclination of the sample to be mounted becomes relatively larger than the unevenness of the sample surface.

In order to address the above problem, conventionally,
The sample stage is provided with a tilting mechanism, and based on the measurement result, the tilt of the sample is eliminated and the measurement is performed again, or a process of correcting the tilt of the sample by software after the measurement is performed. However, such a measure is not appropriate for the purpose of quickly observing a large scanning range, as described with the zooming of the optical microscope as an example.

Further, what is measured in the SPM is three-dimensional information. Conventionally, as described above, for example, black and white shades are associated with height information at a predetermined scanning position on a display screen. . In this case, there is an advantage that a measurement result can be displayed in real time while scanning since no special calculation processing or the like for display is required. However, there is a disadvantage that it is difficult for the measurer to intuitively recognize the three-dimensional shape. Therefore, it is desired to perform three-dimensional stereoscopic display so that the shape can be intuitively recognized.

Further, when measuring a shape in which relatively small irregularities are included in the large irregularities, the contrast of the light and shade with respect to the small irregularities can hardly be recognized.
In some cases, only large irregularities can be recognized.

Therefore, conventionally, three-dimensional stereoscopic display has been performed by processing the data after the measurement is completed and displaying the data in correspondence. For example, a process of calculating the state of light and shadow when the measured surface shape is irradiated with light from a certain direction, performing shading processing, and performing three-dimensional display is employed. Such a process is a commonly used technique, and a description thereof will be omitted. However, since a large amount of computation is required, it is difficult to display the image in real time while scanning. As described, it is not suitable for the purpose of quickly observing a large scanning range.

An object of the present invention is to provide a scanning probe microscope which can solve the above-mentioned problems, can observe a large scanning range quickly, and can easily and quickly perform three-dimensional stereoscopic display. Is to do.

[0016]

In order to achieve the above object, a scanning probe microscope according to the present invention (corresponding to claim 1) has a probe facing a sample and a probe between the sample and the probe. Displacement means (tripods, etc.) for changing the distance of the object
Scanning means for moving the probe relative to the surface of the sample (XY scanning circuit); and detection means for detecting the amount of change in the probe caused by the physical quantity generated between the probe and the sample ( Optical lever detecting device), arithmetic means (subtractor) for obtaining a difference between the amount of change and a reference set value and outputting a deviation signal, and displacement means for inputting the deviation signal so that the deviation signal satisfies an appropriate condition. Control means (control circuit) for controlling the operation of the device, and signal processing means (signal processing apparatus) for processing signals output from each of the scanning means and the control means and displaying a measurement image on a screen of a display means (display device) The scanning probe microscope includes a deviation signal for generating a measurement image using the deviation signal and a signal output from the scanning unit, and displaying the measurement image on a screen of a display unit. Image creation means (deviation signal of signal processing device Configured with the creation processing unit).

In the above configuration, more preferably,
A measurement image is created and displayed by associating the magnitude of the value of the deviation signal with the color information.

In the above arrangement, the scanning means scans at such a high scanning speed that the control by the control means is in a state in which it cannot follow, and a deviation signal is generated.

In a scanning probe microscope, a large scanning range is usually scanned at high speed, and as a result, when control cannot be followed, even if a measurement image is obtained by using a control signal, a measurement error is large and is sufficiently effective. No information available. On the other hand, a deviation signal related to control according to the surface shape is generated as a measurement error. Therefore, the scanning probe microscope of the present invention has a configuration in which the deviation signal is positively used, and a measurement image reflecting the shape of the sample surface is created and displayed using the deviation signal. For example, the magnitude of the deviation signal at a predetermined scanning position is displayed in association with color information.
More specifically, for example, when there is some irregularity in the scanning range of the sample surface, a large control deviation (deviation signal) occurs if the irregularity is large, and if it is small, the relative irregularity is relatively large. And a control deviation does not occur in a flat place. Therefore, even when scanning a large scanning range at high speed, according to the scanning probe microscope of the present invention, by using the deviation signal,
A measurement image corresponding to the surface irregularities can be obtained.

Even when the sample is placed on an inclined plane, for example, if the scanning range is flat without any irregularities, even if scanning is performed at a high speed, the inclination of the sample is a signal component that changes slowly. , The control can follow, no control deviation occurs, and is theoretically always zero. Therefore, in the scanning probe microscope according to the present invention, the tilt component is not displayed, but is canceled, and is displayed as a flat image without tilt and without irregularities. Further, even when the sample is placed on an inclined surface and there is some unevenness on the surface, the tilt component is not displayed for the same reason, but is canceled, and only a measurement image corresponding to the unevenness on the sample surface can be obtained.

Further, for example, consider the control deviation that occurs when scanning a simple symmetric convex shape.
The sign of the control deviation generated at the rising portion (provisionally left) of the convex shape is opposite to the sign of the control deviation generated at the falling portion (provisionally right) of the convex shape. Deviations occur. Further, since control can follow the flat portion on the convex shape and the flat portion other than the convex shape, the control deviation is theoretically zero. In the present invention,
When the magnitude of the signal value of the control deviation generated in such a manner is displayed in association with, for example, black and white shading, the left side of the convex shape is relatively white, the right side is relatively black, and the other flat portions are those flat portions. The image is displayed with a contrast of an intermediate density. Such a display calculates the state when light is irradiated from the left side of the measured convex shape (it should look like a white glow), performs processing such that the right side is dark and shaded, and displays it three-dimensionally. It is substantially equal to the image that has undergone conventional processing. In other words, according to the present invention, it is possible to obtain a measurement image as if it had been subjected to shading processing, by simply creating a measurement image using the deviation signal in the same manner as in the related art, without performing such calculations.

[0022]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of an SPM according to the present invention. The SPM of the present embodiment is of a force detection type having a cantilever as an example, and particularly shows an example of an AFM in a contact mode. Further, in this AFM, the displacement amount caused by the bending deformation of the cantilever is detected by using a general principle of detecting a lever.

In FIG. 1, a sample 11 is placed on a sample table 13 supported by a tripod 12. The tripod 12 includes a three-axis piezoelectric element that supports the sample table 13, that is, an X-axis piezoelectric element 14a, a Y-axis piezoelectric element (not shown), and a Z-axis piezoelectric element 14b. This is a three-dimensional actuator for driving in the Z-axis direction for controlling the distance between (or between the cantilever and the sample). On the upper side of the sample 11, a cantilever 16 having a probe tip 15 facing the sample 11 at the tip is arranged. Above the cantilever 16, an optical lever (optical displacement detection device) including a laser light source 17 and a photodetector 18 is arranged. Laser light 1 emitted from laser light source 17
7 a is reflected on the back surface (mirror surface) of the cantilever 16 and enters the photodetector 18. The sample 11 and the probe 15 are
1 and the probe 15 are kept close to each other to the extent that an atomic force acts, and when the distance between the sample and the probe changes, the interatomic force changes. The cantilever 16 bends and deforms. The amount of displacement generated in the cantilever 16 due to the bending deformation of the cantilever 16 is
It is measured with an optical lever.

In FIG. 1, when measuring the shape of the surface of the sample 11, the probe 15 is brought close to a region where an atomic force acts on the sample 11 by a well-known approach / retreat mechanism (not shown). At that time, the probe 15 receives a force from the sample surface, and the cantilever 16 bends.
The displacement of the cantilever 16 (displacement of the probe 15) detected by the optical lever is extracted from the photodetector 18 as a displacement signal s1. In the subtracter 19, a difference between a preset set value s0 as a reference and the displacement signal s1 is calculated as a deviation signal Δs. The deviation signal Δs is supplied to the control circuit 2
0 is supplied. The control circuit 20 controls the operation of the tripod 12 in the Z-axis direction, that is, the Z-axis piezoelectric element 14b.
A control signal s2 is generated and output so that s becomes 0. That is, in this control system, control is performed such that the displacement amount due to the bending deformation of the cantilever 16 always matches the set value s0. As a result, the probe 15 moves the sample 11
Is kept pressed against the surface by a constant force.
As described above, the tripod 12 is driven by the XY scanning circuit 21 to control the pressing force of the probe 15 against the sample 11 to be constant, and the surface of the sample 11 is
, The control signal s2 in the Z-axis direction changes according to the uneven shape of the surface of the sample 11.

The XY scanning circuit 21 outputs a scanning drive signal for determining a scanning speed. Therefore, the XY scanning circuit 21 has a function of determining the scanning speed.

The signal processing device 22 is composed of a computer or the like, and includes a measurement image creation processing unit 22a and a deviation signal image creation processing unit 22b realized as functional means by a program prepared inside.

The control signal s2 and the scanning drive signal output from the XY scanning circuit 21 are input to a signal processing device 22, and further input to a measurement image creation processing unit 22a. The measurement image creation processing unit 22a obtains the height information of the sample surface by the control signal s2, obtains the position information (coordinate information) in the scanning range from the scanning drive signal, and combines the data relating to these information to generate the measurement image Data for drawing is created, and an image relating to the unevenness information on the sample surface, that is, a measurement image is displayed on the screen of the display device 23 using the data. The measurement image is created and displayed so that the measurer can easily grasp it visually. For example, the height of the unevenness on the sample surface obtained by the control signal s2 is displayed on the screen in association with the density of black and white.

Further, in the configuration of the SPM according to the present embodiment, the deviation signal Δs and the scanning drive signal output from the XY scanning circuit 21 are configured to be input to the deviation signal image creation processing section 22 b of the signal processing device 22. You. The deviation signal image creation processing unit 22b creates a deviation signal image using the deviation signal Δs and the scanning drive signal, and displays the image on the display device 23.

The value of the deviation signal Δs is a reference value s
This is a value obtained by subtracting the actual displacement amount of the cantilever 16 due to the bending deformation, that is, the deformation amount from 0, and corresponds to a measurement error. The deviation signal Δs can be said to be the deformation amount deviation of the cantilever 16. If the control system is an analog control system, the signal to be handled is a voltage signal, and the deviation signal Δs is a voltage signal. The deviation signal Δs is generated when the control by the control system cannot follow.

FIG. 2 shows a case where a certain sample is actually measured by the AFM, and the measured image creation processing section 22a of the signal processing device 22 corresponds to the black and white shading according to the magnitude of the control signal s2 at each measurement point. In addition, a measurement image is created, and the created image is displayed on the screen of the display device 23. White is associated with the highest point in the scanning range and black is associated with the lowest point, and a gray scale corresponding to the height is displayed between the points. In a conventional general AFM, such a measurement image is obtained using the control signal s2. 0.3 μm vertical on the surface of the sample,
There is an elliptical concave shape (recess) having a width of 0.6 μm, and the bottom surface of the depression and portions other than the depression are substantially flat. Therefore,
The inside of the oval is black, and the rest is white. In addition, this sample is placed in a state where the upper right side is inclined about 0.3 μm lower than the lower left side in the figure. Therefore, the lower left is displayed white and the upper right is displayed relatively black.

FIG. 3 shows the state of light and shadow when light is radiated from the lower right direction in the drawing, using the measurement data to create the measurement image of FIG. 2, and the viewpoint at that time is right above. Instead, it calculates the appearance when viewed from a viewpoint slightly inclined to the lower right side, performs shading processing, and stereoscopically displays the image. Since the light is irradiated from the lower right, the left slope of the hollow portion appears to glow white, and the right slope is shaded black.
It can also be seen that the placed sample is inclined from the upper left to the lower right. Furthermore, although it was difficult to understand in FIG. 2, a slightly convex portion (bump) was formed on the upper portion of the depression.
3 can be fully recognized in FIG. In addition, a very small protrusion on the left end and a delicate shape of the slope of the depression cannot be recognized at all in FIG. 2, but can be recognized in FIG. Conventional AFM is
As described above, the apparatus generally has a function of processing in a software manner based on the measurement data and displaying the data three-dimensionally. Such a function is very effective in recognizing the surface shape of the sample.

In this embodiment, as described above, the signal processing device 22 includes the deviation signal image creation processing section 22b. The deviation signal image creation processing unit 22b receives the deviation signal Δs, and displays the deviation signal Δs on the screen of the display device 23 using the deviation signal Δs and the scanning drive signal of the XY scanning circuit 21. The deviation signal image creation processing unit 22b associates black and white shading according to the magnitude of the deviation signal Δs at each measurement point, and creates data for displaying the deviation signal image. The process of creating the deviation signal image is substantially the same as the conventional measurement image creation process performed using the control signal s2, and does not require a particularly complicated operation. Therefore, similarly to the measurement image based on the conventional control signal s2, it is possible to create and display a measurement image based on the deviation signal Δs generated in the control system in real time while scanning.

In the above description, for convenience of explanation, the measurement image creation processing unit 22a using the control signal s2 and the deviation signal Δs
Has been described as a different processing means from the deviation signal image creation processing unit 22b, but the content of the processing is the same, so that the deviation signal can be input to the measurement image creation processing unit 22a, and the measurement image The creation processing unit 22a may be configured to have a function of a deviation signal image creation process.

FIG. 4 shows the above-mentioned certain sample as the A of this embodiment.
FM, and the deviation signal Δs at each measurement point is measured by the deviation signal image creation processor 22b of the signal processor 22.
The deviation signal image is created by associating black and white shading in accordance with the magnitude of the value, and the image is displayed on the screen of the display device 23. White at the point of the largest deviation signal in the scanning range,
Black is associated with the point where the deviation signal is the smallest, and the area between the points is displayed with a gradation corresponding to the height. Also in this case, the deviation signal image is displayed in real time similarly to the measurement image shown in FIG. In particular, when such a deviation signal image can be created and displayed, scanning is performed at a relatively high speed, so that the control system including the control circuit 20 and the like cannot follow and a control deviation (deviation signal Δs) occurs. It is.

The measurement image created using the deviation signal Δs has the following characteristics. Since the bottom surface of the dent and the portion other than the dent are flat, the control can follow, so that the deviation signal Δs is almost zero. In addition, control cannot follow the left slope portion of the dent because the change in height is abrupt, and a control deviation occurs. Similarly, a control deviation occurs in the right slope portion, but the deviation signal Δs Is opposite to that on the left slope. This is because the height decreases sharply when scanning the left slope (in this case, scanning from left to right), but increases rapidly on the right slope. Therefore, in FIG. 4, the left slope portion is white, the right slope portion is black, and a flat portion where the control deviation is almost 0 has a gray level intermediate between white and black. Such a display should appear as if the light and shadow states when light is emitted from the right side are calculated and displayed. Actually, FIG. 4 is a display very similar to the stereoscopic display in FIG. In addition, a slightly convex portion (bump) on the upper portion of the depression which was difficult to understand in FIG.
Also, the small protrusion on the left side can be clearly recognized in FIG. 4 as in FIG. Further, the tilt component of the sample is a gradual change in height over the entire scanning range, so that control can be followed, and therefore the tilt component is canceled in FIG.

In this embodiment, the case where the measurement image based on the control signal s2 and the measurement image (deviation signal image) based on the deviation signal Δs are simultaneously displayed in real time, but only one of them is selected. It is easy to make the display possible.

[0038]

As is apparent from the above description, according to the present invention, an image is created by using the deviation signal generated in the control system in the SPM measurement, for example, by associating the magnitude of the deviation signal with the color information, Since the display is performed, high-speed scanning can be performed to obtain information on the unevenness of the sample surface. In particular, in the case of high-speed scanning in which the original control cannot follow and a control deviation occurs, there is an effect that information on the sample surface can be obtained. The measurement image created using the deviation signal
An image corresponding to the shape of the sample surface can be displayed in real time as a three-dimensionally recognizable image without any special calculation. Therefore, it is possible to quickly perform observation in a relatively large scanning range and easily find a target observation place. Also, the inclined portion when the sample is placed can be canceled without performing special processing.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a scanning probe microscope according to the present invention.

2 shows an example of a measurement image obtained by using the control signal with a scanning probe microscope of the present invention, on the display
It is a photograph of the displayed halftone image.

[3] The three-dimensional image software to create having a slope by using the data of the measurement image shown in FIG. 2, Display
-It is a photograph of the halftone image displayed above.

4 shows an example of a measurement image obtained by using the deviation signal with a scanning probe microscope of the present invention, on the display
It is a photograph of the displayed halftone image.

FIG. 5 is a configuration diagram illustrating an example of a conventional scanning probe microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Sample 12 Tripod 13 Sample stand 15 Probe 16 Cantilever 17 Laser light source 18 Photodetector 22 Signal processing device 22a Measurement image creation processing part 22b Deviation signal image creation processing part 23 Display device

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G12B 21/00-21/24 G01B 21/30 H01J 37/28 JICST file ( JOIS)

Claims (3)

(57) [Claims] A probe facing a sample; a displacement unit configured to change a distance between the sample and the probe; a scanning unit configured to move the probe relative to a surface of the sample;
Detecting means for detecting an amount of change occurring in the probe due to a physical amount occurring between the probe and the sample; calculating means for obtaining a difference between the amount of change and a reference set value and outputting a deviation signal; A control means for inputting a deviation signal and controlling the operation of the displacement means so that the deviation signal satisfies an appropriate condition; a signal processing means for processing signals outputted from each of the scanning means and the control means; In a scanning probe microscope equipped with a signal processing unit for displaying a measurement image, a measurement image is created using the deviation signal and a signal output from the scanning unit, and the measurement image is displayed on a screen of the display unit. A scanning probe microscope comprising a deviation signal image creating means for displaying. 2. The scanning probe microscope according to claim 1, wherein the measurement image is created and displayed in accordance with the magnitude of the value of the deviation signal corresponding to color information. 3. The scanning unit according to claim 1, wherein the control by the control unit is in a state in which the control unit cannot follow, and scans at a high scanning speed such that the deviation signal is generated.
Or the scanning probe microscope according to 2.